An access opening in a firecode wall, which term is here intended to cover a side Wall, floor, or ceiling, must be constructed of fireproof material and in such a manner that it does not open or let fire pass in case of a fire on one side of the wall. Thus it is known to mount on the outside edge of the door or on the inside edge of the opening a strip of foamable material, for instance a specially formulated polystyrene or polyurethane, that will swell and fill any gap between the outer periphery of the panel and the inner periphery of the hole. In case of a fire this material will therefore effectively block passage of anything past the gap around the panel.
The main disadvantage with this arrangement is that the strip is relatively exposed. Even when it is set in a groove of a frame lining the inside of the opening or surrounding the panel edge, it can be damaged relatively easily. Moisture can get to it with ease, and in the normal course of using the access panel it can be damaged to the point where it no longer functions as intended, creating a code violation.